This invention relates generally to the field of semiconductor design and fabrication. Specifically, the invention relates to methods and solutions for cleaning polished metal layers, methods for fabricating metallization structures, and the structures resulting from these methods.
Abrasive planarization (xe2x80x9cAPxe2x80x9d) techniques, such as chemical-mechanical planarization processes, are frequently used to planarize the surface layers of a wafer during fabrication of integrated circuits (ICs). In AP processes, a wafer is generally pressed against a polishing pad in a slurry solution under controlled chemical, pressure, velocity, and temperature conditions. The slurry solution generally contains abrasive particles that mechanically remove the surface layer and may contain chemical agents which attack the surface layer. The polishing pad is generally a planar pad made from a relatively soft, porous material. After being planarized, the surface layer is cleaned to remove materials introduced during the AP process by the slurry, polishing pad, or wafer.
AP processes are particularly useful for planarizing a metallic surface layer to subsequently form conductive features, such as interlayer connectors and conducting lines. Interlayer connectors may be fabricated by forming holes through a dielectric layer, depositing a metal liner over the dielectric layer and in the holes, depositing a metallic layer over the metal liner, and then planarizing the metallic layer to an end-point near the upper surface of the dielectric layer. Conducting lines may be created by forming trenches in a substrate, such as a silicon wafer, depositing a metal liner over the substrate and in the trenches, depositing a metallic layer over the metal liner and in the trenches, and then planarizing the metal layer to an end-point near the upper surface of the substrate. In both instances, the metallic layers are often planarized using slurries that contain abrasive particles such as aluminum oxide (Al2O3) particles.
After the metallic layers are planarized, residual particles from the slurry, polishing pad, or wafer remain on the planarized surface. The residual materials include aluminum oxide particles (also known as alumina) from both the slurry and metallic layer, as well as particles from the dielectric layer. All of these particles cause defects in the planarized surface. Thus, it is necessary to clean these residual particles from the planarized surface. Several methods of post-AP cleaning, such as using hydrofluoric (HF) acid or ammonium hydroxide (NH4OH) solutions, are described in U.S. Pat. Nos. 5,498,293, 5,662,769, and 5,679,169, the disclosures of which are incorporated herein by reference.
One problem with current cleaning processes, at least for planarized aluminum-containing layers, is corrosion of the aluminum surface by the cleaning solution. In current cleaning processes, a wafer containing the planarized aluminum-containing layer is placed in a bath of deionized (DI) water and vibrated with sonic energy to remove loose residual particles from the planarized surface. The DI water unfortunately degrades the exposed aluminum surface by forming a thin native oxide layer and by removing aluminum atoms through diffusion. The corrosion caused by DI water can be xe2x80x9cmousebitexe2x80x9d corrosion, which degrades the interface between the metal and dielectric layers, and xe2x80x9cESD burnoutxe2x80x9d corrosion, which degrades specific features of individual devices presumably by galvanic action. The corrosion becomes more apparent at smaller pitches. Such corrosion results in reduced performance of the integrated circuit.
The present invention includes methods for making an aluminum-containing metallization structure and the metallization structures formed thereby. The methods are practiced by providing a substrate, forming a metal layer with an upper surface containing aluminum over the substrate, polishing the metal layer, and contacting the polished surface of the metal layer with a solution comprising water and at least one corrosion-inhibiting agent. The substrate may be a silicon substrate. The metal layer may be polished by an abrasive planarization process. The corrosion-inhibiting agent may be citric acid or a salt thereof. The solution may contain additional additives, such as chelating agents, buffers, oxidants, anti-oxidants, and surfactants.
The present invention also includes methods for cleaning a polished aluminum-containing layer and the structures formed thereby. The methods are practiced by contacting a polished aluminum-containing layer with a solution comprising water and at least one corrosion-inhibiting agent. The water may be deionized water. The corrosion-inhibiting agent may be citric acid or a salt thereof. The solution may contain additional additives, such as chelating agents, buffers, oxidants, anti-oxidants, and surfactants.
The present invention also includes solutions for cleaning a polished aluminum-containing layer. The solution contains water and at least one corrosion-inhibiting agent. The water may be deionized water. The corrosion-inhibiting agent may be citric acid or a salt thereof. The solution may contain additional additives, such as chelating agents, buffers, oxidants, anti-oxidants, and surfactants.
The present invention reduces corrosion of polished aluminum-containing layers caused by cleaning solutions containing DI water. The present invention also maintains a passivative environment which protects the exposed aluminum structures.